Fluxoid quantization effects in superconducting mesoscopic Al multiloop structures

We have studied fluxoid quantization effects in mesoscopic Al samples consisting of a small number of square loops. In short microladders a pronounced substructure of the Little-Parks oscillations (i.e. the oscillations of the critical temperature Tc as a function of the applied magnetic flux φ) has been found. These new features in Tc(φ) originate from transitions between different quantum states, each having a specific order parameter profile and flow pattern of the supercurrents. The experimental data are in excellent agreement with the Tc(φ) calculated within the de Gennes-Alexander model for superconducting micronetworks. (orig.)